Method, apparatus, and system for implementing a content switch

ABSTRACT

Some embodiments provide a novel content switching method that distributes requests for different types of content to different sets of content servers. In some embodiments, the method deploys a content switch in the ingress data path of a first content server that is part of a first set of servers that processes requests for a first type of content. This content switch receives each content request that is directed to the first content server, and determines whether the received request is for the first content type that is processed by the first content server. If so, the content switch directs the request to the first content server. On the other hand, if the request is for a second type of content that is processed by a second set of servers, the content switch identifies a second content server in the second set and forwards the request to the second content server. When the second set of servers includes two or more servers, the content switch in some embodiments performs a load balancing operation to distribute the load amongst the servers in the second set. For each request, the load balancing operation in some embodiments selects one server from the second server set based on a set of load balancing criteria that specifies one manner for distributing the requests among the servers of the second set, and then forwards the request to the selected server.

CLAIM OF BENEFIT TO PRIOR APPLICATIONS

This application is a continuation application of U.S. patent application Ser. No. 14/813,643, filed Jul. 30, 2015, now published as U.S. Patent Publication 2016/0294935. U.S. patent application Ser. No. 14/813,643 claims the benefit of U.S. Provisional Patent Application 62/142,876, filed on Apr. 3, 2015. U.S. patent application Ser. No. 14/813,643, now published as U.S. Patent Publication 2016/0294935, is incorporated herein by reference.

BACKGROUND

Content switches are typically used to load balance data requests amount a group of servers (e.g., virtual machines) that provide similar services to Internet users. Such servers typically process different types of content. For instance, some servers may have dynamic content (such as URLs with .php, .asp, etc.), other servers have static image content (such as URLs with .jpg, .img, etc.) and yet others have static HTML content (such as URLs with .html). Content switches can also be used to redirect requests to different server pools on the basis of various request attributes, such as: Language, Cookies and Cookie value, HTTP method, and etc.

Today, most content switching architectures rely on one or more content switches that serve as a common node through which the content data requests are funneled. This architecture causes the content switches to serve as chokepoints for the data traffic. This is especially problematic as the volume of data requests is not static and is often hard to predict. Existing content server architectures also do not rapidly adjust to dynamically changing data request volumes.

BRIEF SUMMARY

Some embodiments provide a novel content switching method that distributes requests for different types of content to different sets of content servers. In some embodiments, the method deploys a content switch in the ingress data path of a first content server that is part of a first set of servers that processes requests for a first type of content. This content switch receives each content request that is directed to the first content server, and determines whether the received request is for the first content type that is processed by the first content server. If so, the content switch directs the request to the first content server.

On the other hand, if the request is for a second type of content that is processed by a second set of servers, the content switch identifies a second content server in the second set and forwards the request to the second content server. When the second set of servers includes two or more servers, the content switch in some embodiments performs a load balancing operation to distribute the load amongst the servers in the second set. For each request, the load balancing operation in some embodiments selects one server from the second server set based on a set of load balancing criteria that specifies one manner for distributing the requests among the servers of the second set, and then forwards the request to the selected server.

In some embodiments, the different sets of servers are part of one network (e.g., one datacenter or an associated set of datacenters) and are associated with one common network identifier. One example of a common network identifier is a virtual IP (Internet Protocol) address, also referred to as a VIP address. In some of these embodiments, the network has a set of network devices (e.g., load balancers) that distribute the content requests with this common network identifier amongst the different server sets, without considering the type of content associated with each request.

Therefore, to address the proper distribution of these requests, the method of some embodiments deploys an inline content switch in the ingress data path of each content server, so that the content switch (1) can ensure that its associated content server should process each request that is directed to it, and if not, (2) can direct the requests that are inappropriately directed to it to other content servers that are appropriate for the request's associated content type. To re-direct requests to another content server (i.e., to a content server that is not associated with the content switch), the content switch uses different re-directing mechanisms in different embodiments, such as MAC re-direct, tunnel-enabled re-directs, destination network address translation, etc.

To identify the type of requested content, each inline content switch in some embodiments establishes a layer 4 connection session (e.g., a TCP/IP session) with the source compute node of each request, so that the content switch (1) can receive a first set of one or more payload packets for the session, and (2) can extract the requested content type from the payload packet(s). Because from the perspective of the requesting source compute node the content switch is terminating the layer 4 connection, the content switch then needs (1) to establish a connection session (e.g., through a three-way TCP handshake procedure) with the content server to which it passes the request, and (2) to use this connection session to relay packets that it receives from the source compute node to the content server. In relaying these packets, the content switch in some embodiments might provide sequence number offset to the content server so that the content server can use the correct sequence numbers when providing a response to the source compute node.

When the content switch determines that the request is for a type of content that is processed by a content server associated with the content switch, the content switch passes this request to its associated content sever. However, before passing this request along, the content switch in some embodiments establishes a layer 4 connection session (e.g., by performing 3-way TCP handshake) with the associated content server because the content switch terminated the connection with the source compute node that sent the request. In other embodiments, the content switch does not establish a layer 4 connection session with its associated content server, because this server is configured to use the content switch to establish layer 4 connection sessions.

In some embodiments, the inline content switches implement a conceptual distributed content switch (also called a logical content switch) that ensures that requests for different types of content are appropriately directed to different sets of content servers. By having these content switches perform load balancing operations to distribute the requests that they re-direct between different servers in a server set, this logical content switch also serves as a logical load balancer that distributes the load amongst the servers within each set of servers. Like its associated logical content server, the logical load balancer is also a conceptual load balancer that is implemented by several load balancers that are distributed along the ingress data path of the content servers.

The logical content switch of some embodiments is implemented in a datacenter with multiple host computing devices (hosts) that execute severs and software forwarding elements (SFEs). In some embodiments, the servers are virtual machines (VMs) and/or containers that execute on the hosts. These servers include content servers. In some embodiments, content servers from the same set or from different sets can execute on the same host or on different hosts.

An SFE (e.g., a software switch and/or router) on a host is a module that communicatively couples the servers of the host to each other and/or to other devices (e.g., other servers) outside of the host. In some embodiments, the SFE implements the content switch operation of the server. In other embodiments, each server's content switch is a module that is inserted in the ingress path of the server before or after the SFE. For instance, in some embodiments, each server has a virtual network interface card (VNIC) that connects to a port of the SFE. In some of these embodiments, the content switch for the server is called by the server's VNIC or by the SFE port to which the server's VNIC connects. Other embodiments implement the distributed content switches differently. For instance, in some embodiments, two or more content servers on one host use one content switch that is inserted in the servers' ingress data paths before or after an SFE in these paths.

A set of one or more controllers facilitate the operations of the distributed content switch (DCS) and/or distributed load balancing (DLB) of some embodiments. For instance, in some embodiments, the controller set provides to each inline content switch a set of rules that identify the sets of content servers, the servers in each set, and the types of content processed by each server set. In some embodiments, the controller set provides the rules and/or configuration data directly to the inline content switches, while in other embodiments it provides this information to content switch agents that execute on the hosts and these agents relay the appropriate data to the content switches.

For the load balancing operations, load balancing statistics are gathered on the hosts based on the data messages that are directed to the content servers. The collected statistics are then passed to the controller set, which aggregates the statistics. In some embodiments, the controller set then distributes the aggregated statistics to the hosts (e.g., to agents, load balancers, or content switches on the hosts), where the aggregated statistics are analyzed to generate and/or to adjust load balancing criteria that are enforce. In other embodiments, the controller set analyzes the aggregated statistics to generate and/or to adjust load balancing criteria, which the controller set then distributes to the hosts for the load balancers to enforce. In still other embodiments, the controller set generates and distributes some load balancing criteria based on the aggregated statistics, while other load balancing criteria are adjusted on the hosts based on distributed aggregated statistics.

Irrespective of the implementation for generating the load balancing criteria, the collection and aggregation of the data traffic statistics allows the load balancing criteria to be dynamically adjusted. For instance, when the statistics show that one content server is too congested with data traffic, the load balancing criteria can be adjusted dynamically to reduce the load on this content server while increasing the load on one or more content server in the same set. In some embodiments, the collection and aggregation of the data traffic statistics also allows the method to reduce the load in any load balanced content server set by dynamically instantiating or allocating new content servers for the server set. Analogously, when the load on a content server set reduces (e.g., falls below a certain threshold), the method can remove or de-allocate content servers from the server set.

The preceding Summary is intended to serve as a brief introduction to some embodiments of the invention. It is not meant to be an introduction or overview of all inventive subject matter disclosed in this document. The Detailed Description that follows and the Drawings that are referred to in the Detailed Description will further describe the embodiments described in the Summary as well as other embodiments. Accordingly, to understand all the embodiments described by this document, a full review of the Summary, Detailed Description, the Drawings and the Claims is needed. Moreover, the claimed subject matters are not to be limited by the illustrative details in the Summary, Detailed Description and the Drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth in the appended claims. However, for purposes of explanation, several embodiments of the invention are set forth in the following figures.

FIG. 1 illustrates a distributed content switch that implements the content switching method of some embodiments.

FIG. 2 illustrates another distributed content switching architecture of some embodiments of the invention.

FIGS. 3 and 4 present two messaging diagrams that illustrate two different ways that a distributed content switch (DCS) filter of FIG. 2 can facilitate the relaying of the content request packets to an image server.

FIG. 5 illustrates that the DCS filters of the hosts implement a distributed content switch (i.e., a logical content switch) that ensures that requests for different types of content are appropriately directed to different sets of content servers.

FIG. 6 illustrates a more detailed architecture of a host that executes the DCS filters of some embodiments of the invention.

FIG. 7 conceptually illustrates a process that a DCS filter performs in some embodiment when it receives a new content request.

FIG. 8 illustrates an example of a DCS controller set that configures the DCS filters and their associated load balancers.

FIG. 9 illustrates a process that one or more controllers in the controller set perform in some embodiments.

FIG. 10 conceptually illustrates an electronic system 1000 with which some embodiments of the invention are implemented.

DETAILED DESCRIPTION

In the following detailed description of the invention, numerous details, examples, and embodiments of the invention are set forth and described. However, it will be clear and apparent to one skilled in the art that the invention is not limited to the embodiments set forth and that the invention may be practiced without some of the specific details and examples discussed.

Some embodiments provide a novel content switching method that distributes requests for different types of content to different sets of content servers. In some embodiments, the method deploys a content switch in the ingress data path of a first content server that is part of a first set of servers that processes requests for a first type of content. This content switch receives each content request that is directed to the first content server, and determines whether the received request is for the first content type that is processed by the first content server. If so, the content switch directs the request to the first content server.

On the other hand, if the request is for a second type of content that is processed by a second set of servers, the content switch identifies a second content server in the second set and forwards the request to the second content server. When the second set of servers includes two or more servers, the content switch in some embodiments performs a load balancing operation to distribute the load amongst the servers in the second set. For each request, the load balancing operation in some embodiments (1) selects one server from the second server set based on a set of load balancing criteria that specifies one manner for distributing the requests among the servers of the second set, and then (2) forwards the request to the selected server.

Two sets of content servers can differ in a variety of ways. For instance, in some embodiments, different sets of content servers are differentiated based on the type of content that they process, e.g., a first content server set that processes requests for image files, a second content server set that processes requests for video files, and a third content server set that processes requests for HTML files. Different content server sets can also be different based on the type of operation they perform. For example, in some embodiments, a first set of content servers perform database (e.g., SQL) read operations, while a second set of content servers perform database (e.g., SQL) write operations. More generally, content request can be grouped based on any number of request attributes (such as language, cookies, cookie values, HTTP method, etc.), and different content server sets can be defined to process different groups of requests.

FIG. 1 illustrates a content switch 100 that implements the content switching method of some embodiments. Specifically, this figure illustrates two content switches 100 and 105 that are two software modules that execute on two host computing devices 110 and 115 along with several servers. The servers include non-content servers 120 and content servers, which in this example include a set of HTML servers 125 and a set of image servers 130. In some embodiments, the servers are virtual machines (VMs) that execute on the hosts, while in other embodiments, the servers are containers that execute on the hosts. As shown, content servers from different sets (e.g., HTML server set) can execute on the same host or on different hosts. Similarly, content servers from the same set can execute on the same host or on different hosts.

In some embodiments, the content servers (i.e., the HTML servers 125 and image servers 130) are collectively addressed by a common network identifier in the content requesting data messages. For instance, in some embodiments, each content requesting data message collectively addresses all of the content servers by using one virtual IP address that is associated with all of the content servers. As used in this document, a data message refers to a collection of bits in a particular format sent across a network. One of ordinary skill in the art will recognize that the term data message may be used herein to refer to various formatted collections of bits that may be sent across a network, such as Ethernet frames, IP packets, TCP segments, UDP datagrams, etc. Also, as used in this document, references to second, third, and fourth layers (or L2, L3, and L4) layers are references respectively to the second data link layer, the third network layer, and the fourth transport layer of the OSI (Open System Interconnection) layer model.

In FIG. 1, each content switch 100 or 105 on each host 110 or 115 performs its content switching operation for all of the content servers on its host. As further described below, other embodiments deploy a unique content switch for each content server. In the example illustrated in FIG. 1, the content switch 100 of host 110 receives two content requests 150 and 155 at two different instances in time. The content request 150 is a request for HTML content, while the content request 155 is a request for image content. Both of these requests are part of data messages that identify all the content servers collectively, e.g., by using the content server VIP address as the destination IP address in the data packet headers. FIG. 1 uses different types of legends to illustrate the two different types of requests and the responses to these requests. Specifically, it shows white circles and squares to pictorially represent the HTML requests and HTML responses respectively, while using cross-hatched circles and squares to pictorially represent the image requests and image responses respectively.

As shown in FIG. 1, the content switch 100 forward the HTML request 150 to one of the HTML servers 125 a on its host, because after examining this request, it determines that the request is for content that one of its content servers processes. As further described below, a content switch in some embodiments has to perform a “soft” termination of the connection session (i.e., has to establish a layer 4 connection session (e.g., a TCP/IP session)) with the source compute node that sent the content request, so that the content switch can receive one or more payload packets for the session, in order to extract the requested content type from the payload packet(s). As shown, after providing the HTML request 150 to the HTML server 125 a, the content switch 100 receives the requested HTML content 160 from the HTML server 125 a, and directs this response to the requesting device (not shown) through an intervening network fabric (not shown).

On the other hand, after receiving the image request 155, the content switch determines that this request is not for content that one of its servers processes, identifies host 115 as a host that has an image server that handles image requests, and re-directs the image request 155 to the host 115. To re-direct the image request to host 115, the content switch 100 uses different re-directing mechanisms in different embodiments, such as MAC re-direct, tunnel-enabled re-directs, destination network address translation, etc. At host 115, the content switch 105 determines that the request 155 is for content that one of its content servers processes, and forwards the image request 155 to one of its image servers 130 a. In response, the image server 130 a provides the requested image content 165 to the content switch 105, which then directs this response to the requesting device (not shown) through an intervening network fabric (not shown).

As further shown in FIG. 1, the content switches 100 and 105 implement a distributed content switch 190 that ensures that requests for different types of content are appropriately directed to different sets of content servers. In the discussion below, a distributed content switch is also referred to as a logical content switch as it is not a single physical switch in a physical world, but rather is a conceptual construct that describes the collective operation of multiple different physical constructs (e.g., multiple different content software switches, software filters, etc.). FIG. 1 shows the conceptual distributed content switch directing the HTML request 150 to HTML server 125 a, directing the image request 155 to image server 130 a, and directing the responses 160 and 165 from these servers to the requesting servers (not shown) through intervening network fabric (not shown).

FIG. 2 illustrates another distributed content switching architecture of some embodiments of the invention. In this architecture, the distributed content switching operation is performed by several content switching filters that execute on several hosts in a datacenter 290. As shown, the datacenter includes several host computing devices 200, a set of load balancers 205, and intervening network fabric 210 that connects the hosts 200 and the load balancer set 205. Each host computing device (host) executes a software forwarding element 215, several content servers 220 and 225, and a distributed content switch (DCS) filter 230 for each content server.

In this example, the content severs are HTML servers 220 and image servers 225. In some embodiments, the servers are virtual machines (VMs) and/or containers that execute on the hosts. As shown, content servers from different sets (e.g., HTML server set) can execute on the same host or on different hosts. Similarly, content servers from the same set can execute on the same host or on different hosts.

The content servers are connected to each other, to other resources on the hosts, and to the load balancer set 205 through software forwarding elements 215 and the intervening network fabric 210. Examples of software forwarding elements 215 include software switches and/or software routers. Intervening network fabric 210 in some embodiments includes switches, routers, and other network devices that operate outside of the hosts.

In the distributed content switching architecture of FIG. 2, one DCS filter 230 is placed between each content server (e.g., a server 220 or 225) and the SFE 215 on the server's host. In some embodiments, each content server's DCS filter is just placed in the ingress data path of the server (i.e., each DCS filter is not in the egress data path between the server and the SFE). Each content server's DCS filter examines content requests that the SFE forwards to the content server and determines whether the received request is for a content type that is processed by the filter's associated content server. If so, the DCS filter 230 directs the request to its content server. On the other hand, when the request is for a type of content that is not processed by the filter's server, the DCS filter 230 identifies another content server to process the request and forwards the request to this other server.

In some embodiments, a content request might be inappropriately sent to the wrong content server because (1) the different sets of content servers are associated with one common network identifier (such as one VIP address) and (2) the load balancer set 205 distributes the content requests with the common network identifier amongst all the content servers without identifying the type of content that is needed for processing each request. For instance, in some embodiments, the load balancer set distributes each content request (e.g., each data packet that has the content-server VIP address as its destination IP address in its packet header) based on a hash of the packet's five-tuple identifiers (i.e., a hash of the source IP address, destination IP address, source port, destination port, and protocol) without considering the type of content that is requested. Therefore, to address the proper distribution of these requests, each DCS filters of some embodiments (1) examines each request that it receives for its content server to determine whether its server should process the request, and if not, (2) directs the request that is inappropriately directed to its server to another content server that is appropriate for the request's associated content type.

In the example illustrated in FIG. 2, the load balancer set 205 sends to the HTML server 220 a two content requests 250 and 255 at two different instances in time. The first content request 250 is a request for HTML content, while the second content request 255 is a request for image content. Both these requests are part of data packets addressed to the VIP address associated with all the content servers. FIG. 2 uses different types of legends to illustrate the two different types of requests and the responses to these requests. Specifically, it shows white circles and squares to pictorially represent the HTML requests and HTML responses, while using cross-hatched circles and squares to pictorially represent the image requests and image responses. Moreover, in this example, the order of the request/response message flow is identified by the sequence of numbers that is illustrated next to each version of the request or response message as it is passes between the illustrated components (e.g., between the load balancer(s), the network fabric, or software modules).

As shown in FIG. 2, the DCS filter 230 a forward the HTML request 250 to its HTML server 220 a, because after examining this request, it determines that the request is for content that its content server processes. As further described below, a DCS filter (like filter 230 a) in some embodiments has to perform a “soft” termination of the connection session (i.e., has to establish a layer 4 connection session (e.g., a TCP/IP session)) with the source compute node of the content request, so that the DCS filter can receive one or more payload packets for the session, in order to extract the requested content type from the payload packet(s). As shown, after providing the HTML request 250 to the HTM server 220 a, the HTML server 220 a provides the requested HTML content 260 to the SFE 215 a, which then directs this response to the requesting device (not shown) through an intervening network fabric 210.

On the other hand, upon receiving the image request 255, the DCS filter 230 a determines that this request is not for content that its HTML server 220 a processes, selects the image server 225 a as the image server for processing this image request, identifies the host 200 b as a host on which the image server 225 a executes, and re-directs the image request 255 to the image server 225 a by re-directing it to the SFE 215 b of the host 200 b. To re-direct the image request to host 200 b, the DCS filter 230 a uses a tunnel 285 that is established between the SFE 215 a on the host 200 a and the SFE 215 b on the host 200 b.

To use the tunnel, the DCS filter 230 a in some embodiments encapsulates the packets that it receives from the requesting source compute node (SCN) with a packet header for the tunnel, and then provides the encapsulated packets to the SFE 215 a to forward to the SFE 215 b. Instead of directly encapsulating the re-directed packets, the DCS filter 230 a in other embodiments has another filter module (e.g., another module associated with server 220 a) encapsulate the re-directed packets with the packet header for the tunnel. In still other embodiments, the DCS filter 230 a uses different re-directing mechanisms to re-direct the image requests to the host 200 b. For instance, in other embodiments, the DCS filter 230 a uses MAC re-direct (i.e., changes the destination MAC address in each packet header from the MAC address associated with HTML server 220 a to the MAC address associated with image server 225 a), or use DNAT re-direct (i.e., changes the destination IP address in each packet header from the IP address associated with HTML server 220 a to the IP address associated with image server 225 a). In yet other embodiments, the DCS filter 230 a has the SFE 215 a encapsulate the tunnel packet headers or perform the MAC/DNAT re-direct to relay the re-directed data packets to the host 200 b.

At host 200 b, the SFE 215 b in some embodiments provides the image request 255 to the DCS filter 230 b of the image server 225 a, and this filter forwards the image request 255 to its image server 225 a after determining that the request 255 is for image content that its server processes. Alternatively, in other embodiments, the SFE 215 b is configured to directly provide to the image server 225 a (without going through the DCS filter 230 b) packets that the SFE 215 b receives for the image server 225 a through the tunnel 285 from the SFE 215 a. In still other embodiments, the SFE 215 b is configured to provide the packets that it receives through the tunnel 285 for the image server 225 a to the DCS filter 230 b, but the DCS filter 230 b is configured to simply pass redirected image requests (e.g., as indicated by a parameter that the SFE passes to it) to the image server 225 a without examining the packets to determine whether they are for image content processed by the server 225 a. After receiving the image request 255, the image server 225 a provides the requested image content 265 to the SFE 215 b, which then directs this response 265 to the requesting device (not shown) through an intervening network fabric 210.

As mentioned above, a DCS filter in some embodiments has to establish a layer 4 connection session (e.g., a TCP/IP session) with the requesting SCN (i.e., the SCN that sent the content request), so that the DCS filter can receive one or more payload packets for the session, in order to extract the requested content type from the payload packet(s). When the DCS filter determines that it needs to direct the content request to another content server (i.e., a content server that is not associated with the DCS filter), the DCS filter in some embodiments establishes a layer 4 connection session with the other content server, and then uses this connection to relay the packets that it receives from the requesting SCN to the other content server.

For the example illustrated in FIG. 2, FIGS. 3 and 4 present two messaging diagrams that illustrate two different ways that the DCS filter 230 a can facilitate the relaying of the content request packets (i.e., the re-directed packets from the requesting SCN) to the image server 225 a. As shown, in both the messaging flows, the DCS filter 230 a first establishes a TCP session with the SCN by performing a 3-way TCP handshake. Both messaging flows show the front end load balancer set 205 with dotted lines in order to emphasize that this load balancer set forwards the packets from the SCN to the DCS filter 230 a.

After establishing the TCP session, the DCS filter 230 a identifies the type of content that is being requested from the first packet or the first few packets. In some embodiments, one manner that the DCS filter 230 a uses to identify the content type is by extracting the URL (Uniform Resource Locator) and/or URL parameters that are contained in the first packet or the first few packets. The URL and/or URL parameters often contain the name or acronym of the type of content being requested (e.g., contain .mov, .img, .jpg, or other similar designations that identify the requested content).

As shown in both the messaging flows, the DCS filter 230 a starts to relay the packets that it receives from the SCN to the image server 225 a after identifying that the content request is for image data and determining that the image server 225 a should process such a request. As further shown, the messaging flows in the examples of FIGS. 3 and 4 diverge in how they provide the response packets from the image server 225 a to the SCN. In FIG. 3, these response packets are sent directly from the image server 225 a to the SCN, while in FIG. 4, the response packets are first sent to the DCS filter 230 a, which then relays them to the SCN.

In some embodiments, for the response packet approach of FIG. 3, the DCS filter 230 a provide a TCP sequence number offset to the image server 325 a, so that the image server can use this offset in adjusting its TCP sequence numbers that it uses in its reply packets that respond to packets from SCN. In some embodiments, the DCS filter 230 a provides the TCP sequence number offset in the encapsulating tunnel packet header of the tunnel 285 that is used to relay packets from the DCS filter 230 a to the image server 225 a. In some embodiments, the DCS filter 230 a also performs some TCP sequence number adjusting as it relays packets between a SCN and a content server. The DCS filter performs these adjustments because different sequence numbers might be used for the two different TCP sessions that the DCS filter has with the SCN and has with the content server.

FIG. 5 illustrates that the DCS filters 230 of the hosts 200 implement a distributed content switch 590 (i.e., a logical content switch) that ensures that requests for different types of content are appropriately directed to different sets of content servers. Specifically, this figure shows the conceptual distributed content switch 590 directing the HTML request 250 to HTML server 220 a, directing the image request 255 to image server 225 a, and directing the responses 260 and 265 from these servers to the requesting servers (not shown) through intervening network fabric (not shown).

In some embodiments, each DCS filter 230 not only performs a content switch operation for its content server, but also perform a load balancing operation that distributes the content request load amongst another set of servers when the filter has to re-direct the received content requests to servers in the other set. For each re-directed request, the load balancing operation of the DCS filter in some embodiments (1) selects one server from the other server set based on a set of load balancing criteria that specifies one manner for distributing the requests among the servers of the other set, and then (2) forwards the request to the selected server. For instance, to re-direct the image request 255 to one of the image servers in the image server set, the DCS filter 230 a first performs a load balancing operation that identifies the imager server 225 a as the image server that should receive the request 255, and then re-directs this request to the image server 225 a.

By having these content switches perform load balancing operations to distribute the requests that they re-direct between different servers in a server set, the logical content switch also serves as a logical load balancer that distributes the load amongst the servers within each set of servers that receives the re-directed data messages. FIG. 5 identifies the distributed content switch 590 as also a distributed load balancer (DLB) because, in this example, the DCS filters 230 perform load balancing operations when they re-direct to other servers requests that they receive. Like a logical content server, the logical load balancer is also a conceptual load balancer that is implemented by several DCS filter load balancers that are distributed along the ingress data path of the content servers.

In contrast to traditional centralized content switching and load balancing architectures that have content switches and load balancers that are chokepoints for traffic, the distributed content switch architecture of FIGS. 2 and 5 does not have data traffic chokepoints. Also, this distributed architecture is ideally suited for the unpredictable number of requests and clients that may exist at any one time. Because of its distributed nature, this architecture is able to handle very high performance requirements (e.g., high TCP connection per second and high HTTP request per second).

One other aspect of this high-performance architecture that makes it ideally suitable for the unpredictable nature of data traffic flow is that in this architecture, the sets of content servers are dynamically adjustable based on the data traffic flow. In other words, servers can be elastically added or removed to each content server set based on the changing nature of the data traffic flow. Also, the load balancing operation of the DCS filters can be modified to change how the filters distribute load amongst the content servers in one set.

To dynamically adjust the content server sets, the network controllers of the distributed content switching architecture of some embodiments (1) gather data regarding traffic flow, (2) based on the gathered data, modify one or more sets of content servers, and/or (3) adjust dynamically the configuration of the DCS filters to modify their load balancing operations for distributing the load across one or more content server sets and/or to account for the modifications to the server sets in performing their content switching and/or load balancing operations. The elastic nature of this architecture will be further described below.

FIG. 6 illustrates a more detailed architecture of a host 600 that executes the DCS filters of some embodiments of the invention. As shown, the host 600 executes multiple VMs 605, an SFE 610, multiple DCS filters 630, multiple load balancers 615, an agent 620, and a publisher 622. The host also has a DCS rule storage 650, a load balancing (LB) rule storage 652, a statistics (STAT) data storage 654, group membership data storage 684, policy data storage 682, aggregated (global) statistics data storage 686, and connection state storage 690.

In some embodiments, the VMs execute on top of a hypervisor, which is a software layer that enables the virtualization of the shared hardware resources of the host. In some of these embodiments, the hypervisors provide the DCS filters in order to support inline content switching services to its VMs.

The SFE 610 executes on the host to communicatively couple the VMs of the host to each other and to other devices outside of the host (e.g., other VMs on other hosts) through one or more forwarding elements (e.g., switches and/or routers) that operate outside of the host. As shown, the SFE 610 includes a port 632 to connect to a physical network interface card (not shown) of the host, and a port 635 that connects to each VNIC 625 of each VM. In some embodiments, the VNICs are software abstractions of the physical network interface card (PNIC) that are implemented by the virtualization software (e.g., by a hypervisor). Each VNIC is responsible for exchanging data messages between its VM and the SFE 610 through its corresponding SFE port. As shown, a VM's ingress datapath for its data messages includes (1) the SFE port 632, (2) the SFE 610, (3) the SFE port 635, and (4) the VM's VNIC 625.

Through its port 632 and a NIC driver (not shown), the SFE 610 connects to the host's PNIC to send outgoing packets and to receive incoming packets. The SFE 610 performs message-processing operations to forward messages that it receives on one of its ports to another one of its ports. For example, in some embodiments, the SFE tries to use header values in the VM data message to match the message to flow based rules, and upon finding a match, to perform the action specified by the matching rule (e.g., to hand the packet to one of its ports 632 or 635, which directs the packet to be supplied to a destination VM or to the PNIC). In some embodiments, the SFE extracts from a data message a virtual network identifier (VNI) and a MAC address. The SFE in these embodiments uses the extracted VNI to identify a logical port group, and then uses the MAC address to identify a port within the port group. In some embodiments, the SFE 610 is a software switch, while in other embodiments it is a software router or a combined software switch/router.

The SFE 610 in some embodiments implements one or more logical forwarding elements (e.g., logical switches or logical routers) with SFEs executing on other hosts in a multi-host environment. A logical forwarding element in some embodiments can span multiple hosts to connect VMs that execute on different hosts but belong to one logical network. In other words, different logical forwarding elements can be defined to specify different logical networks for different users, and each logical forwarding element can be defined by multiple SFEs on multiple hosts. Each logical forwarding element isolates the traffic of the VMs of one logical network from the VMs of another logical network that is serviced by another logical forwarding element. A logical forwarding element can connect VMs executing on the same host and/or different hosts.

The SFE ports 635 in some embodiments include one or more function calls to one or more modules that implement special input/output (I/O) operations on incoming and outgoing packets that are received at the ports. One of these function calls for a port is to a DCS filter 630. In some embodiments, the DCS filter performs the content switch operations on incoming data messages that are addressed to the filter's VM. In some embodiments, one or more load balancers 205 (e.g., one or more load balancing appliances) in the datacenter 200 distribute content requests that are addressed to the VIP address of all content servers among the content serving VMs without regard to the content request type and the type of contents that the content serving VMs process. In some embodiments, the load balancer 205 directs a content request packet to one of the content serving VM by changing the destination MAC address of packet to the MAC address of the VM. In other embodiments, the load balancer 205 directs a content request packet to one of the content serving VM by changing the destination IP address of packet to the IP address of the VM.

In the embodiments illustrated in FIG. 6, each port 635 has its own DCS filter 630. In other embodiments, some or all of the ports 635 share the same DCS filter 630 (e.g., all the ports on the same host share one DCS filter, or all ports on a host that are part of the same logical network share one DCS filter).

Examples of other I/O operations that are implemented through function calls by the ports 635 include firewall operations, encryption operations, message encapsulation operations (e.g., encapsulation operations needed for sending messages along tunnels to implement overlay logical network operations), etc. By implementing a stack of such function calls, the ports can implement a chain of I/O operations on incoming and/or outgoing messages in some embodiments. Instead of calling the I/O operators (including the DCS filter 630) from the ports 635, other embodiments call these operators from the VM's VNIC or from the port 632 of the SFE.

The DCS filters 630 perform their content switching operations based on the DCS rules that are specified in the DCS rule storage 650. For different types of content requests, the DCS rule storage 650 stores the identity of different content server (CS) sets. For each new content request flow, a DCS filter 630 identifies the requested content type. When its VM processes the identified requested content type, the DCS filter passes the content request to its VM. On the other hand, when the identified requested content type is not one that its VM processes, the DCS filter re-directs this request to another VM.

To perform this re-direction, the DCS filter 630 examines its DCS rule storage 650 to identify the CS set that processes the identified, requested content type. Also, for this re-direction, the DCS filter 630 in some embodiments performs a load balancing operation to distribute the re-directed content request that it sends to the identified CS set among the servers in the set. To perform its load balancing operation for the servers of the identified CS sets, each DCS filter 630 has a load balancer 615 that the filter uses to identify one content server in the identified CS set for each new content request packet flow that the DCS filter has to re-direct. In other embodiments, all the DCS filters use the same load balancer 615, or multiple DCS filters use one load balancer 615 (e.g., DCS filters of VMs that are part of one logical network use one load balancer 615 on each host).

A load balancer 615 selects one content server from an identified CS set (i.e., a CS set identified by a DCS filter) based on the LB rules that are specified in the LB rule storage 652. For one load balanced CS set, the LB rule storage 652 stores a load balancing rule that specifies one or more physical addresses (e.g., IP addresses) of content server(s) of the set to which a data message can be re-directed. More specifically, in some embodiments, the LB rule storage 652 stores multiple LB rules, with each LB rule associated with one load balanced CS set. In some embodiments, each LB rule includes (1) the identifier of a CS set, (2) an address for each server in the CS set.

In some embodiments, the server addresses in a LB rule are the IP addresses of these servers. In some embodiments, the content server addresses are supplied as a part of the data initially supplied by a controller set (e.g., in order to configure the load balancer) or are supplied in subsequent updates to the CS set information that is provided by the controller set. Also, in some embodiments, for each identified content server, the LB rule specifies the tunnel to use to send a re-directed packet to the content server. In some embodiments, an LB rule can specify different re-direction mechanisms for accessing different content servers, as not all content servers are accessible through the same re-direction mechanism.

After the DCS filter identifies the CS set that should process a content request that it needs to re-direct, the filter in some embodiments provides the CS set identifier to the load balancer, so that the load balancer can use this identifier to identify the LB rule that it needs to use to select a content server in the CS set. In some embodiments, each LB rule stores the load balancing criteria that the load balancer 615 has to use to select one of the content servers of the CS set.

For instance, in some embodiments, the load balancers 615 use a weighted round robin scheme to select the content servers. Accordingly, in some of these embodiments, each LB rule stores a weight value for each content server specified in the LB rule, and the weight values provides the criteria for the load balancer to spread the traffic to the content servers of the CS set associated with the rule. For example, assume that the CS set has five servers and the weight values for these servers are 1, 3, 1, 3, and 2. Based on these values, a load balancer would distribute content requests that are part of ten new content request flows as follows: 1 to the first content server, 3 to the second content server, 1 to the third content server, 3 to the fourth content server, and 2 to the fifth content server. In some embodiments, the weight values for an LB rule are generated and adjusted by the agent 620 and/or a controller set based on the statistics that DCS filters store in the STAT data storage 654, as further described below.

To gracefully switch between different load balancing criteria, an LB rule in some embodiments can specify time periods for different load balancing criteria of the LB rule that are valid for different periods of time. Specifically, in some embodiments, each LB rule can have multiple sets of IP addresses and multiple sets of weight values. Each set of IP addresses and its associated set of weight values represents one set of load balancing criteria. For each of these sets of load balancing criteria, each rule has a time value that specifies the time period during which the IP address set and its associated weight value set are valid.

For instance, in an LB rule, the time value for one IP address set might specify “before 1 pm on 9/1/2015,” while the time value for another IP address set might specify “after 12:59 pm on 9/1/2015.” These two time periods allow the load balancers to seamlessly switch from using one IP address set and its associated weight value set to another IP address set and its associated weight value set at 1 pm on 9/1/2015. These two IP address sets might be identical and they might only differ in their associated weight value sets. Alternatively, the two IP address sets might be different. Two IP address sets might differ but have overlapping IP addresses (e.g., one set might have five IP addresses, while another set might have four of these five IP addresses when one content server is removed from a CS set). Alternatively, two IP address sets might differ by having no IP addresses in common.

As shown in FIG. 6, the host also includes a connection state storage 690 in which a DCS filter stores data records that allow the DCS filter to maintain connection state for data messages that are part of the same flow, and thereby to distribute data messages that are part of the same flow statefully to the same content server. More specifically, whenever the DCS filter 630 passes a content request to its associated VM, the DCS filter stores a record with the identifier of its associate VM in the connection state storage 690 so that it can identify its associated VM for subsequent data messages that are part of the same flow. Also, whenever the DCS filter 630 uses a load balancer to identify another content serving VM to receive a re-directed content request, DCS filter not only sends the re-directed content request to the identified content serving VM, but also stores a record in the connection state storage 690 to identify (e.g., in terms of the other content serving VM's IP address) the other content serving VM for subsequent data messages that are part of the same flow.

Each flow's record in the connection state storage 690 not only stores the identity of the content server (e.g., the identifier of filter's own VM or the destination IP address of another content server) but also stores the flow's header values (e.g., the five tuple values). In some embodiments, for fast access, the connection data storage 690 is hash indexed based on the hash of the header values of the flows for which the storage 690 has records.

To identify a content server for a received data message, the DCS filter first checks the connection state storage 690 to determine whether it has previously identified a content server for receiving data messages that are in the same flow as the received message. If so, the DCS filter uses the content server that is identified in the connection state storage. Only when the DCS filter does not find a connection record in the connection state storage 690, the DCS filter in some embodiments examines the packet payload to identify the type of content being requested, and then if needed examines the DCS rules and in some cases the LB rules (in the DCS and LB rule storages 650 and 652) in order to identify a content server to receive the data message.

By searching the connection state storage 690 with the message identifiers of subsequent data messages that are part of the same flow, the DCS filter can identify the content server that it previously identified for a data message of the same flow, in order to use the same content server for the messages that are part of the same flow (i.e., in order to statefully perform its content switching operation). In some embodiments, the DCS filter also uses the connection state storage 690 records to replace the content server's destination address with the virtual group address (e.g., the group VIP address) on the reverse flow path when the DCS filter receives (from the SFE port 630 or 635) data messages sent by the content server to the source compute node that requested the content. After translating of the destination addresses of a data message in the reverse flow, the DCS filter returns the data message to the SFE port that called it, so that the SFE port can direct the data message to source compute node.

In FIG. 6, only one LB rule data storage 652 and only one connection state storage 690 are illustrated for all load balancers 615 and the DCS filters 630. In other embodiments, each DCS filter has its own connection state storage 690 and each load balancer has its own LB rule storage 652. When each load balancer 615 has its own rule data storage 652 and each DCS filter has its own connection state storage 690, these storages can be smaller and easier to search more quickly. In yet other embodiments, the host has several rule data storages 652 or connection state storages 690, but two or more load balancers or DCS filters share a rule data storage or connection state storage (e.g., two load balancers or DCS filters that are balancing the load for two VMs that are part of the same logical network).

In some embodiments, each time a DCS filter performs a content switching operation on a data message (i.e., directs a message to a content serving VM), the DCS filter updates the statistics that it maintains in the STAT data storage 654 for the data traffic that it relays to the content servers. Examples of such statistics include the number of data messages (e.g., number of packets), data message flows and/or data message bytes relayed to each content server. In some embodiments, the metrics can be normalized to units of time, e.g., per second, per minute, etc.

In some embodiments, the agent 620 gathers (e.g., periodically collects) the statistics that the DCS filters store in the STAT data storage(s) 654, and relays these statistics to a controller set. Based on statistics that the controller set gathers from various agents 620 of various hosts, the controller set (1) distributes the aggregated statistics to each host's agent 620 so that each agent can define and/or adjust the load balancing criteria of the load balancers on its host, and/or (2) analyzes the aggregated statistics to specify and distribute some or all of the load balancing criteria for the load balancers to enforce. In some embodiments where the controller set generates the load balancing criteria from the aggregated statistics, the controller set distributes the generated load balancing criteria to the agents 620 of the hosts.

In the embodiments where the agent 620 receives new load balancing criteria from the controller set, the agent 620 stores these criteria in the host-level LB rule storage 688 for propagation to the LB rule storage(s) 652. In the embodiment where the agent 620 receives aggregated statistics from the controller set, the agent 620 stores the aggregated statistics in the global statistics data storage 686. In some embodiments, the agent 620 analyzes the aggregated statistics in this storage 686 to define and/or adjust the load balancing criteria (e.g., weight values), which it then stores in the LB rule storage 688 for propagation to the LB rule storage(s) 652. The publisher 622 retrieves each LB rule and/or updated load balancing criteria that the agent 620 stores in the LB rule storage 688, and stores the retrieved rule or criteria in the LB rule storage 652 of the load balancer 615 that needs to enforce this rule.

The agent 620 not only propagates LB rule updates based on newly received aggregated statistics, but it also propagates LB rules or updates LB rules based on updates to CS sets that it receives from the controller set. The agent 620 stores each CS set's members that it receives from the controller set in the group data storage 684. When a content server is added or removed from a CS set, the agent 620 stores this update in the group storage 684, and then formulates updates to the LB rules to add or remove the destination address of this content server to or from the LB rules that should include or already include this address. Again, the agent 620 stores such updated rules in the rule data storage 688, from where the publisher propagates them to the LB rule storage(s) 652 of the load balancers that need to enforce these rules.

When a content server is added to a CS set, the updated LB rules cause the load balancers to direct some of the CS set's data messages to the added content server. Alternatively, when a content is removed from a CS set, the updated LB rules cause the load balancers to re-direct data messages that would go to the removed content server, to other content servers in the CS set. Even after a content server is intentionally designated for removal from a CS set, a DCS filter in some embodiments may continue to send data messages (e.g., for a short duration of time after the removal of the content server) to the content server that are part of prior flows that were directed to the content server. This allows the content server to be removed gradually and gracefully from the CS set as the flows that it handles terminate. Some embodiments also achieve a graceful transition away from a content server that should be removed from the CS set by using time values to specify when different LB criteria for the same LB rule should be used. Some embodiments also use such time values to gracefully add a new content server to a CS set.

In some embodiments, the agent 620 stores in the policy storage 682, LB policies that direct the operation of the agent (1) in response to newly provisioned content server VMs and their associated DCS filters and/or load balancers, and/or (2) in response to updated global statistics, LB criteria, and/or adjusted CS set membership. The policies in the policy storage 682 in some embodiments are supplied by the controller set. Also, in some embodiments, the agent 620 stores and updates content server identities and content types processed by these servers in the DCS rule storage 650.

FIG. 7 conceptually illustrates a process 700 that a DCS filter 630 performs in some embodiment when it receives a new content request data message. As shown, the process 700 starts whenever the DCS filter receives a new content request, which is a content request for which the DCS filter's connection storage 690 does not have a record that identifies a VM to process the request. As mentioned above, one or more load balancers 205 (e.g., one or more load balancing appliances) in the datacenter 200 distribute in some embodiments the content requests that are addressed to the VIP address of all content servers among the content serving VMs without regard to the content request type and the type of contents that the content serving VMs process.

In some embodiments, a new content request starts with a request for a layer 4 connection session. After receiving the new content request, the DCS filter 630 in some embodiments establishes (at 710) a layer 4 connection session with the requesting SCN (i.e., the SCN that sent the content request), so that the DCS filter can receive one or more payload packets for the session, in order to extract the requested content type from the payload packet(s). To establish a connection session, the DCS filter 630 establishes in some embodiments a TCP session with the SCN by performing a 3-way TCP handshake.

After establishing the connection session, the DCS filter 630 identifies (at 710) the type of content that is being requested from the first payload packets or the first few payload packets. In some embodiments, one manner that the DCS filter 230 a uses to identify the content type is by extracting the URL and/or URL parameters that are contained in the payload packet(s). The URL and/or URL parameters often contain the name or acronym of the type of content being requested (e.g., contain .mov, .img, .jpg, or other similar designations that identify the requested content).

After identifying the content type, the DCS filter 630 then determines (at 715) whether its associated VM (e.g., the VM that has its VNIC 625 associated with the SFE port 635 that called the DCS filter) is a content server that processes the requested content type. If so, the DCS filter 630 passes (at 720) the initial content request packet and subsequent content request packets that are part of the same flow to its associate VM and then ends. The DCS filter also stores (at 720) in its connection state storage 690 a record that it can subsequently use to identify its VM as the content server for other content request data messages that are part of the same flow.

When the DCS filter determines (at 715) that the request is for a type of content that is processed by its associated VM, the filter in some embodiments establishes (at 720) a layer 4 connection session (e.g., by performing 3-way TCP handshake) with its associated VM before passing this request along to the VM. This is because the DCS filter terminated the connection with the requesting SCN. In other embodiments, the DCS filter does not establish a layer 4 connection session with its associated VM, because this VM is configured to use the DCS filter to establish layer 4 connection sessions.

When the DCS filter 630 determines (at 715) that its associated VM is not a content server that processes the requested content type, the DCS has to re-direct the content request packet to another content server (i.e., to a content server that is not associated with the DCS filter). To re-direct the content request packet, the DCS filter first identifies (at 725) a CS set that processes the content type identified at 710. The DCS filter then directs (at 725) its load balancer to select one content server in the identified CS set. When the CS set has more than one content servers, this load balancer's selection is based on a set of load balancing criteria that specifies one manner for distributing the requests among the servers of the CS set identified at 725. On the other hand, when the CS set only has one content server, the load balancer simply selects that server. In some embodiments, the DCS filter has the addresses of the content servers and hence does not use the load balancer when the identified CS set only has one server.

After identifying a content server to which it can send the re-directed content request, the DCS filter 630 establishes (at 730) a layer 4 connection session with this content server, because the DCS filter terminated the connection session with the requesting SCN and because of this termination the content server does not have a connection session with the SCN. To establish this connection session, the DCS filter 630 in some embodiments establishes a TCP session with the content server by performing a 3-way TCP handshake.

After establishing (at 730) the connection session with the identified content server (i.e., the VM identified at 725), the DCS filter 630 uses this session (at 735) to relay the content request that it receives from the requesting SCN to the content server. As mentioned above, the DCS filter can use different re-directing mechanisms in different embodiments (such as MAC re-direct, tunnel-enabled re-directs, destination network address translation, or any combination of these) to forward the content request to the identified content server. In forwarding the content request, the content switch in some embodiments provides a TCP sequence number offset to the identified content server so that the content server can use the correct sequence numbers when providing a response to the source compute node directly. In some embodiments, the DCS filter 630 provides the sequence number offset in the encapsulating tunnel packet header of the tunnel that is used to relay packets from the DCS filter 630 to the identified content server.

When only one tunnel is established between each pair of hosts, multiple candidate content servers can be on a host. In these situations, the receiving host's SFE (i.e., the SFE of the host that receives the re-directed content request) might need to forward different content requests to different content serving VMs on its host. To address this situation, the DCS filter inserts in the tunnel packet header the IP address of the content server that should receive a re-directed content request.

At 735, the DCS filter also stores in its connection state storage 690 a record that it can subsequently use to identify the VM identified at 725 as the content server for other content requests that are part of the same flow as the request received at 705. After 735, the process ends.

FIG. 8 illustrates an example of a DCS controller set 820 that configures the DCS filters 630 and their associated load balancers 615. The controller set 820 also gathers statistics from hosts and based on the gathered statistics, dynamically adjusts the membership of the CS sets and the operations of the load balancers. Specifically, this figure illustrates a multi-host system 800 of some embodiments.

As shown, this system includes multiple virtualized hosts 805-815, a set of DCS controllers 820, and a set of one or more VM managing controllers 825. As shown in FIG. 8, the hosts 805-815, the DCS controller set 820, and the VM manager set 825 communicatively couple through a network 875, which can include a local area network (LAN), a wide area network (WAN) and/or a network of networks (e.g., Internet). In some embodiments, the hosts 805-815 are similar to the host 600 of FIG. 6. However, in FIG. 8, not all of the software modules and storages of the hosts 805-815 are shown in order to simplify the illustration in this figure.

The VM managing controllers 825 provide control and management functionality for defining (e.g., allocating or instantiating) and managing one or more VMs on each host. These controllers in some embodiments also provide control and management functionality for defining and managing multiple logical networks that are defined on the common software forwarding elements of the hosts, while in other embodiments, this functionality is provided by the DCS controller set 820. In some embodiments, the VM managing controllers and the DCS controllers are the same set of controllers.

The DCS controller set 820 configures the DCS filters 630 (e.g., by providing identities of the CS sets, servers in these sets and the types of content processed by these sets) and their associated load balancers 615. This controller set 820 also gathers statistics from hosts and based on the gathered statistics, dynamically adjusts the membership of the CS sets and the operations of the load balancers. Specifically, as mentioned above, each host's agent 620 gathers the collected statistics from the STAT data storage 654 (not shown in FIG. 8), and relays these statistics to the DCS controller set 820. In some embodiments, the agents 620 aggregate and/or analyze some of the statistics before relaying processed statistics to the DCS controller set 820, while in other embodiments the agents relay collected raw statistics to the DCS controller set 820.

The DCS controller set 820 aggregates the statistics that it receives from the agents of the hosts. In some embodiments, the DCS controller set 820 then distributes the aggregated statistics to the agents that execute on the hosts. These agents then analyze the aggregated statistics to generate and/or to adjust LB rules or criteria that the load balancers (that execute on the same hosts as the agents) enforce.

In other embodiments, the controller set analyzes the aggregated statistics to generate and/or to adjust LB rules or criteria, which the controller set then distributes to the agents 620 of the hosts for their load balancers to enforce. In some of these embodiments, the controller set distributes the same LB rules and/or criteria to each load balancer in a group of associated load balancers (i.e., in a group of load balancers that are associated with one group of DCS filters of one CS set), while in other embodiments, the controller distributes different LB rules and/or criteria to different load balancers in the group of associated load balancers. Also, in some embodiments, the controller set distributes updated LB rules and/or criteria to some of the load balancers in an associated group of load balancers, while not distributing the updated LB rules and/or criteria to other load balancers in the associated group.

In still other embodiments, the controller set generates and distributes some load balancing rules or criteria based on the aggregated statistics, while also distributing some or all aggregated statistics to the hosts so that their agents can generate other load balancing rules or criteria. One of ordinary skill in the art will realize that in some embodiments the LB rules and/or criteria are not always adjusted based on the aggregated statistics, but rather are modified only when the aggregated statistics require such modification.

Irrespective of the implementation for generating the LB rules, the collection and aggregation of the data traffic statistics allows the LB rules or criteria to be dynamically adjusted. For instance, when the statistics show one content server as being too congested with data traffic, the LB rules or criteria can be adjusted dynamically for the load balancers of the DCS filters that send data messages to this content server, in order to reduce the load on this content server while increasing the load on one or more other content servers in the same CS set. In some embodiments, the collection and aggregation of the data traffic statistics also allows the controller set 820 to reduce the load on any content server in a load balanced CS set by dynamically directing the VM managing controller set 825 to instantiate or allocate new content serving VMs for the CS set. Analogously, when the load on a content server set reduces (e.g., falls below a certain threshold), the controller set 820 can direct the VM managing controller set 825 to remove or de-allocate content servers from the server set.

FIG. 9 illustrates a process 900 that one or more controllers in the DCS controller set 820 perform in some embodiments. The controller set performs this process to distribute global statistics, group membership updates for a CS set, and/or DCS filter configuration data (e.g., CS set identifiers and associated content type for each identified CS set). As shown, the process 900 starts (at 905) when it (1) receives statistics about content server data processing load (e.g., from one or more agents 620 or load balancers 615), and/or (2) receives membership updates for a CS set (e.g., from the VM managing controller set 825). In some embodiments, the process 900 is also performed when the DCS filters of a host or series of hosts are configured initially (e.g., upon the configuration of one or more hosts, one or more content servers on one or more hosts, etc.).

The process 900 in some embodiments receives (at 905) the group membership updates from a VM managing controller 825 when it informs the process 900 that a content server has been added to a CS set when a new content server has been created for the CS set, or has been removed from the CS set when the content server has been terminated or has failed in the CS set. In some embodiments, the VM managing controller 825 instantiates a new content server or allocates a previously instantiated content server to the CS set at the direction of the process 900, as further described below.

At 910, the process updates (1) the global statistics that the controller set 820 maintains for the CS set based on the statistics received at 905, (2) the CS set's membership that the controller set maintains based on the group updates received at 905, and/or (3) the DCS filter configuration data that it maintains. Next, at 915, the process determines based on the updated statistics whether it should have one or more content server specified or removed for the group. For instance, when the updated statistics causes the aggregated statistics for the CS set to exceed a threshold load value for one or more content servers in the group, the process 900 determines that one or more new content servers have to be specified (e.g., allotted or instantiated) for the CS set to reduce the load on content servers previously specified for the group. Conversely, when the updated statistics shows that a content server in a CS set is being underutilized or is no longer being used to handle any flows, the process 900 determines (at 915) that the content server has to be removed for the CS set. In some embodiments, process 900 also determines that CS set membership should be modified when it receives such a request from a DCS filter 630 or from a host agent 620.

When the process 900 determines (at 915) that it should have one or more content servers added to or removed from a CS set, the process requests (at 920) one or more VM managers 820 to add or remove the content server(s), and then transitions to 925. As mentioned above, the VM managers in some embodiments are one or more servers that are outside of the controller set 825 that handles the DCS and LB data collection and data distribution. In other embodiments, however, a VM manager is a process that one or more controllers in the DCS controller set 825 execute.

The process 900 also transitions to 925 when it determines (at 915) that no content server needs to be added to or removed from a CS set. At 925, the process determines whether the time has reached for it to distribute DCS filter configuration data, membership update and/or global statistics to one or more agents executing on one or more hosts. The DCS filter configuration data is different in different embodiments. For example, as mentioned above, the DCS filter configuration in some embodiments includes the CS set identifiers and associated content type for each identified CS set.

In some embodiments, the process 900 distributes DCS filter configuration data, membership updates and/or global statistics on a periodic basis. In other embodiments, however, the process 900 distributes DCS configuration data, membership update and/or global statistics for the CS set whenever this data is modified. When the process determines (at 925) that it does not need to distribute new data, it transitions to 930 to determine whether it has received any more statistic, membership updates, or DCS configuration data for which it needs to update its records. If so, the process transitions back to 910 to process DCS filter configuration data, the newly received statistic, and/or membership updates. If not, the process transitions back to 925 to determine again whether it should distribute new data to one or more agents.

When the process determines (at 925) that it should distribute membership update(s) DCS filter configuration data and/or global statistics, it distributes (at 935) this data to one or more agents that need to process this data to specify and/or update the DCS filter configuration data and/or load balancing rules that they maintain for their DCS filters and/or load balancers on their hosts. After 935, the process determines (at 940) whether it has to process DCS filter configuration data, or process new statistic or membership data. If not, the process remains at 940 until it determines that it needs to process new DCS filter configuration data and/or process new statistics or membership data, at which time it transitions back to 910 to process the DCS filter configuration data, new statistics and/or membership updates.

In the embodiments described above by reference to FIG. 9, the controller set distributes global statistics to the agents, which analyze this data to specify and/or adjust the DCS configuration data and/or LB rules that they maintain. In other embodiments, however, the controller set analyzes the global statistics that it gathers, and based on this analysis specifies and/or adjusts DCS configuration data or LB rules, which it then distributes to the agents 615, DCS filters 630 or load balancers 620.

Many of the above-described features and applications are implemented as software processes that are specified as a set of instructions recorded on a computer readable storage medium (also referred to as computer readable medium). When these instructions are executed by one or more processing unit(s) (e.g., one or more processors, cores of processors, or other processing units), they cause the processing unit(s) to perform the actions indicated in the instructions. Examples of computer readable media include, but are not limited to, CD-ROMs, flash drives, RAM chips, hard drives, EPROMs, etc. The computer readable media does not include carrier waves and electronic signals passing wirelessly or over wired connections.

In this specification, the term “software” is meant to include firmware residing in read-only memory or applications stored in magnetic storage, which can be read into memory for processing by a processor. Also, in some embodiments, multiple software inventions can be implemented as sub-parts of a larger program while remaining distinct software inventions. In some embodiments, multiple software inventions can also be implemented as separate programs. Finally, any combination of separate programs that together implement a software invention described here is within the scope of the invention. In some embodiments, the software programs, when installed to operate on one or more electronic systems, define one or more specific machine implementations that execute and perform the operations of the software programs.

FIG. 10 conceptually illustrates an electronic system 1000 with which some embodiments of the invention are implemented. The electronic system 1000 can be used to execute any of the control, virtualization, or operating system applications described above. The electronic system 1000 may be a computer (e.g., a desktop computer, personal computer, tablet computer, server computer, mainframe, a blade computer etc.), phone, PDA, or any other sort of electronic device. Such an electronic system includes various types of computer readable media and interfaces for various other types of computer readable media. Electronic system 1000 includes a bus 1005, processing unit(s) 1010, a system memory 1025, a read-only memory 1030, a permanent storage device 1035, input devices 1040, and output devices 1045.

The bus 1005 collectively represents all system, peripheral, and chipset buses that communicatively connect the numerous internal devices of the electronic system 1000. For instance, the bus 1005 communicatively connects the processing unit(s) 1010 with the read-only memory 1030, the system memory 1025, and the permanent storage device 1035.

From these various memory units, the processing unit(s) 1010 retrieves instructions to execute and data to process in order to execute the processes of the invention. The processing unit(s) may be a single processor or a multi-core processor in different embodiments.

The read-only-memory (ROM) 1030 stores static data and instructions that are needed by the processing unit(s) 1010 and other modules of the electronic system. The permanent storage device 1035, on the other hand, is a read-and-write memory device. This device is a non-volatile memory unit that stores instructions and data even when the electronic system 1000 is off. Some embodiments of the invention use a mass-storage device (such as a magnetic or optical disk and its corresponding disk drive) as the permanent storage device 1035.

Other embodiments use a removable storage device (such as a floppy disk, flash drive, etc.) as the permanent storage device. Like the permanent storage device 1035, the system memory 1025 is a read-and-write memory device. However, unlike storage device 1035, the system memory is a volatile read-and-write memory, such a random access memory. The system memory stores some of the instructions and data that the processor needs at runtime. In some embodiments, the invention's processes are stored in the system memory 1025, the permanent storage device 1035, and/or the read-only memory 1030. From these various memory units, the processing unit(s) 1010 retrieves instructions to execute and data to process in order to execute the processes of some embodiments.

The bus 1005 also connects to the input and output devices 1040 and 1045. The input devices enable the user to communicate information and select commands to the electronic system. The input devices 1040 include alphanumeric keyboards and pointing devices (also called “cursor control devices”). The output devices 1045 display images generated by the electronic system. The output devices include printers and display devices, such as cathode ray tubes (CRT) or liquid crystal displays (LCD). Some embodiments include devices such as a touchscreen that function as both input and output devices.

Finally, as shown in FIG. 10, bus 1005 also couples electronic system 1000 to a network 1065 through a network adapter (not shown). In this manner, the computer can be a part of a network of computers (such as a local area network (“LAN”), a wide area network (“WAN”), or an Intranet, or a network of networks, such as the Internet. Any or all components of electronic system 1000 may be used in conjunction with the invention.

Some embodiments include electronic components, such as microprocessors, storage and memory that store computer program instructions in a machine-readable or computer-readable medium (alternatively referred to as computer-readable storage media, machine-readable media, or machine-readable storage media). Some examples of such computer-readable media include RAM, ROM, read-only compact discs (CD-ROM), recordable compact discs (CD-R), rewritable compact discs (CD-RW), read-only digital versatile discs (e.g., DVD-ROM, dual-layer DVD-ROM), a variety of recordable/rewritable DVDs (e.g., DVD-RAM, DVD-RW, DVD+RW, etc.), flash memory (e.g., SD cards, mini-SD cards, micro-SD cards, etc.), magnetic and/or solid state hard drives, read-only and recordable Blu-Ray® discs, ultra density optical discs, any other optical or magnetic media, and floppy disks. The computer-readable media may store a computer program that is executable by at least one processing unit and includes sets of instructions for performing various operations. Examples of computer programs or computer code include machine code, such as is produced by a compiler, and files including higher-level code that are executed by a computer, an electronic component, or a microprocessor using an interpreter.

While the above discussion primarily refers to microprocessor or multi-core processors that execute software, some embodiments are performed by one or more integrated circuits, such as application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs). In some embodiments, such integrated circuits execute instructions that are stored on the circuit itself.

As used in this specification, the terms “computer”, “server”, “processor”, and “memory” all refer to electronic or other technological devices. These terms exclude people or groups of people. For the purposes of the specification, the terms display or displaying means displaying on an electronic device. As used in this specification, the terms “computer readable medium,” “computer readable media,” and “machine readable medium” are entirely restricted to tangible, physical objects that store information in a form that is readable by a computer. These terms exclude any wireless signals, wired download signals, and any other ephemeral signals.

While the invention has been described with reference to numerous specific details, one of ordinary skill in the art will recognize that the invention can be embodied in other specific forms without departing from the spirit of the invention. In addition, a number of the figures conceptually illustrate processes. The specific operations of these processes may not be performed in the exact order shown and described. The specific operations may not be performed in one continuous series of operations, and different specific operations may be performed in different embodiments. Furthermore, the process could be implemented using several sub-processes, or as part of a larger macro process. Thus, one of ordinary skill in the art would understand that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims. 

We claim:
 1. A method of distributing content requests directed to a plurality of content-serving machines including content-serving first and second machines executing on first and second host computers, the method comprising: at the first host computer executing the content-serving first machine, establishing a first layer four (L4) connection session with a third machine that sends a request for content, and using the first L4 connection to identify additional information about the request; based on the additional information, determining that the content-serving second machine should process the request; in response to the determination, establishing a second L4 connection session with the content-serving second machine to forward the request; and identifying a sequence number offset that expresses a difference between a first sequence number value used for the first L4 connection session and a second sequence number value used for the second L4 connection session, and using the sequence number offset to compute the sequence numbers used in data messages from the content-serving second machine to the third machine.
 2. The method of claim 1, wherein the request is a first request, the method further comprising: at the first host computer, establishing a L4 connection session with a fourth machine that sends a second request for content, and using the L4 connection to identify additional information about the second request; based on the additional information, determining that the content-serving first machine should process the second request; and in response to the determination, forwarding the second request to the content-serving first machine to process the second request.
 3. The method of claim 1, wherein the request for content is received in a packet and the additional information is identified by extracting the additional information from a payload of the packet that contains the request.
 4. The method of claim 3, wherein the payload comprises a URL (Uniform Resource Locator) that specifies a type of the requested content; the extracted information comprises the URL, said determining comprises using the extracted URL to select the content-serving second machine for processing the request, as the content-serving second machine processes request for the type specified by the URL.
 5. The method of claim 1 further comprising performing a load balancing operation to select the content-serving second machine from a group of content-serving machines that are for processing requests having a similar type to the received request.
 6. The method of claim 5, wherein the request is for a particular type of content, and the group of content-serving machines processes requests for the particular type of content.
 7. The method of claim 6, wherein the content-serving first machine does not process requests for the particular type of content.
 8. The method of claim 5, wherein the load balancing criteria is defined to spread the load on the content-serving machines in the group of content-serving machines.
 9. The method of claim 1, wherein the content-serving first and second machines are virtual machines executing on first and second host computers, and the establishing, determining, and identifying operations are performed by a module in an ingress path of the content-serving first machine.
 10. The method of claim 9, wherein the module implements a distributed content switch with other modules executing on other host computers and processes packets passing along ingress paths to other content-serving machines executing on the other host computers.
 11. A non-transitory machine readable medium storing a program for execution by at least one processing unit of a first host computer to distribute content requests directed to a plurality of content-serving machines including content-serving first and second machines executing on first and second host computers, the program comprising sets of instructions for: establishing a first layer four (L4) connection session with a third machine that sends a request for content, and using the first L4 connection to identify additional information about the request; based on the additional information, determining that the content-serving second machine should process the request; in response to the determination, establishing a second L4 connection session with the content-serving second machine to forward the request; and identifying a sequence number offset that expresses a difference between a first sequence number value used for the first L4 connection session and a second sequence number value used for the second L4 connection session, and using the sequence number offset to compute the sequence numbers used in data messages from the content-serving second machine to the third machine.
 12. The non-transitory machine readable medium of claim 11, wherein the request is a first request, the program further comprising sets of instructions for: establishing a L4 connection session with a fourth machine that sends a second request for content, and using the L4 connection to identify additional information about the second request; based on the additional information, determining that the content-serving first machine should process the second request; and in response to the determination, forwarding the second request to the content-serving first machine to process the second request.
 13. The non-transitory machine readable medium of claim 11, wherein the request for content is received in a packet and the additional information is identified by extracting the additional information from a payload of the packet that contains the request.
 14. The non-transitory machine readable medium of claim 13, wherein the payload comprises a URL (Uniform Resource Locator) that specifies a type of the requested content; the extracted information comprises the URL, the set of instructions for determining comprises a set of instructions for using the extracted URL to select the content-serving second machine for processing the request, as the content-serving second machine processes request for the type specified by the URL.
 15. The non-transitory machine readable medium of claim 11, wherein the program further comprises a set of instructions for performing a load balancing operation to select the content-serving second machine from a group of content-serving machines that are for processing requests having a similar type to the received request.
 16. The non-transitory machine readable medium of claim 15, wherein the request is for a particular type of content, and the group of content-serving machines processes requests for the particular type of content.
 17. The non-transitory machine readable medium of claim 16, wherein the content-serving first machine does not process requests for the particular type of content.
 18. The non-transitory machine readable medium of claim 15, wherein the load balancing criteria is defined to spread the load on the content-serving machines in the group of content-serving machines.
 19. The non-transitory machine readable medium of claim 11, wherein the content-serving first and second machines are virtual machines executing on first and second host computers, and the sets of instructions for the establishing, determining, and identifying operations are executed by a module in an ingress path of the content-serving first machine.
 20. The non-transitory machine readable medium of claim 19, wherein the module implements a distributed content switch with other modules executing on other host computers and processes packets passing along ingress paths to other content-serving machines executing on the other host computers.
 21. The method of claim 1, wherein using the sequence number offset comprises providing the sequence number offset to the content-serving second machine for the third machine to use to compute the sequence numbers in the data messages that the third machine forwards directly to the content-serving second machine.
 22. The method of claim 1, wherein using the sequence number offset comprises: using the sequence number offset at the first host computer to adjust the sequence number of data messages received at the first host computer from the content-serving second machine in response to the request for content from the third machine; forwarding the data messages with the adjusted sequence numbers from the first host computer to the third machine. 